Pic kit 2 clone vdd short when troubleshooting

I've made a bunch of clones and the problems you are having sound like you have a bad solder joint.
And how are you reading the voltage with the software or are you testing the ISCP pins.

Just as an update . It turns out that although the results were valid,I gave you instead of q6 as requested q4 results ,which would have the 11.5v on it. Tested q4 and found that as expected no 11v across this only vdd which is low due to low usb voltage.rb4 output as predicted high when vdd not on and low when vdd on as you said. Sorry for the confusion .Just to see if I could read a chip,proved unsuccessful as the vdd was too low, when provided by clone 4.17 volts measured, at terminals of pic chip to be read.

It has been hinted at in previous post replies, to change some components .Especially the op amp, which does not have a 5 volt supply to it or the micro controller.The op amp may not be able to supply enough output to supply vdd.I suspect that the pic kit software, may be acting up and leading me to suspect, it is a hardware fault instead it is reading low voltages or non expectant voltages. I have not tried powering the chip from an external 5 volt source to see if it can read or program a chip that way.Unfortunately all the computers I have tried this clone on have low output usb voltages.The caviot of using the pic kit 2 software is having to recalibrate the unit every time you plug it in or in a different computer.

Member be80be, the voltages are being measured with a voltmeter at the icsp pins . The pic kit software is being used to check calibration and to see if the vdd voltage varies as expected.

I am building a stripped down version of a pic kit clone without variable vdd just to prove the thing actually works. I know not all circuits on the internet work first time.
This in some cases can be attributed to, user construction errors and poor soldering.
I have had my fair share of fails, but have persevered and got it working in the end . The circuit I have posted so many times about, I think is working but due to low usb voltages,stands no chance of working with the pic kit software .Being mislead by software and it's inherent foiballs instead of trusting in the hardware being used.

I've never seen low usb stop a piclit clone from working I've used junk parts and plain old npn and pnp transistors and with usb as low as 4.5 volts it still worked.
I use a 3.3 volt suppl for the 3 volt chips and it always worked. I made my own from the sch out the pickit2 and looking at Bills junebug.
I put these together on bread boards and the work fine. Only time one didn't work it was a late night miss wire and a bad ICSP cable. plus one time I used a USB cord that was made for charging didn't let the USB work right Post some good pictures of what you have made.

Have had success with a clone on a breadboard using npn and pnp transistors.Only difference is this one does not vary vdd . Will try the problematic clone with mplab software and see how I get on.Thanks be80be for the words of wisdom and encouragement.

The simple diy Pk2 circuit I posted has run via a 3v3 regulator to program a 3v3 chip without problems several times, so that disproves your theory.
(using a standard 2550 chip as well, not the LF version)

A common problem with with the Pk2/3 programmers is if you have leads from the Pickit to the actual target device of more than 150mm, then weird problem can be given.
Also some chips seem more prone to errors on longer leads than others; no mention of what chips you are using during your tests ?

No chip has been connected, through any of my problems and lead lengths, don't even come into it either.The issue I have is the usb voltage, measured at the pins of the op amp and microcontroller, never make it to vdd output and that is due in part to the op amp rail limit.Others have had to change components to get results that work. External power for vdd ensures this problem is eliminated .The chip can be read if vdd is powered by the target and not by the pic kit clone.

There something wrong how Q6 is being powered the gate needs to be pulled up the the USB 5 volts with a 10 K and a 2.7 or 2.2 on the gate.

My circuit uses transistors and NO diodes and is much simpler. See Talking electronics website.
The skill in electronics is to design something simple.

PIC-2 USB Burner

Your kind of lying there just a little the led is a diode

Finally there is light at the end of a very long tunnel !!! I can confirm that the clone can read, erase and identify a chip in this case a pic 18f 2550, but only when vdd is supplied by the target and not the clone. The external / target supply is simply three AA batteries in series supplying a healthy 4.7 volts. When vdd is supplied by the clone, it can only supply a maximum of 4.35 volts at the icsp pin 2.The pic kit 2 software displays the device not found error , immediately throwing up a vdd error check device or target message.

The op amp used in my circuit is an mcp 602 package . The voltage supplying it and the microcontroller from the usb is 4.75 volts .The output of q1 never gets any where near this value due to op amp rail limits. After this voltage has dropped even furthur across d1 a BAT 85 schottky the voltage is only 4.35 volts. I am sorry to disagree with previous post replies but to read a device successfully the vdd voltage is important and in my case components used , voltage drops and the like are causing problems for an otherwise simple proven circuit that others have built with no issues. Why should I be any different !!

be80be it would seem from what you have said previously, there is an error in the schematic I am using . Which schematic are you using or referring to ? Why would it be such a departure from mine I wonder ?

Colin, you have every right to disagree with suggestion. But after a week more you would agree. After all it is question of concept and you would realize the concept sooner. all the best.

i suppose that no one has established on the said site that the design worked flawless for them.
It is your assumption.at the time of calibration, you were expected to record the voltage measured in to a box and let me hope that you did that and went ahead to other stages.
then you are expected to select the device as pic18F or mod range for the many pic16F series ones.

i had issues, as I told you with 2n7000(BS170) and BS250, they cant deliver proper load. i had changed over to si2303and NDS356 both sot23 and mounted them on copper side..

I accept concepts and take them on board very quickly.Unfortunately what works for one doesn't work for everybody. Everyone who posts on blogs,chat rooms and forums have valid points to make. It has never and will ever be my intention to belittle ,berate or ignore any help or information shared.Sometimes you can try and take notice of too many, and end up more confused than if you hadn't asked anything at all.Some have limited experience myself included,hence all the posts.

The internet is a wonderful tool for learning .Conflicting opinion based on people's own experiences, or the lack thereof muddies the waters however.My only goal,is to build something that works as expected.As others have eluded to they have built clones without issue.You have had to change components.It has a lot to do with which circuit you have chosen to build also.

Know one is sitting on your side of the keyboard. But Im sure that your VDD is dropping out if you get a error witch means you lost power to the target.
This is the sch https://www.obddiag.net/prog/pickit2.pdf I'm talking about

be80be just to clarify pull up resistor on gate of q6 to 5v. What is the 2.2 or 2.7 from the gate for and where is it connected ? I am assuming this is instead of the connection from the op amp or aswell as ?

If you make changes as in blue wiring you should have a working pickitclone the unmarked resistor is 2.7 k

Burt,
I suppose the port b4 takes care of this situation.. Even otherwise it is already there in the form of R6,D4.
Do we need another pull up?

Hi Burt,
As Q6 is a P channel mosfet we need to drive the gate low to turn it on. The pic port output is active high and active low so it should not need either a pull up or pull down resistor. I asked the OP about 5 days ago in post #11 to measure the voltages on gate source and drain of Q6. under the conditions when it was giving a reasonable Vdd output and when is was reporting a short. (I am ASSUMING that he was using the first test for Vdd in the troubleshooting section under the Tools menu.) He measured the voltages on a different mosfet. He has not yet carried out this test and reported the results so we still do not have information to diagnose the problem. Also I agree with Sarma that the BS250 is not the ideal component for Q6. It should work with when the voltage on it's source pin is 5 volts but if the voltage from the variable voltage supply (IC2 and Q1) is set to 3.3 volts or lower and the BS250 has the worst case threshold voltage of 3.5 volts then Q6 would not turn on. Sarma suggested some more suitable devices in post #12. The OP also seems to be ignoring this advice. Until the OP starts giving accurate information and answering questions I am giving up on trying to solve his problems.

Les.